1. Field of the Invention
This invention relates to a copper-based alloy that has a superior balance of conductivity, tensile strength and bending workability and to a method of manufacturing same, and more specifically to a copper-based alloy for use in consumer products, for example, for forming blanks for narrow-pitch connectors for use in telecommunications, blanks for automotive harness connectors, blanks for semiconductor lead frames and blanks for compact switches and relays and the like and a method of manufacturing same.
2. Background Art
Against the background of recent developments in portable and mobile electronic equipment, where the pin thickness and pin width of connectors mounted in computers, mobile phones, digital video cameras and the like are typically 0.10-0.30 mm, there is a trend for these to become even thinner and narrower as the final product is made more compact. As a result of higher volumes of information being input/output through each of these pins at higher data rates, the Joule heat arising from the ON current causes the temperature of the contacts to increase, sometimes even exceeding the temperature tolerance of the insulation enclosing the contacts. Moreover, some of the pins are used for supplying power, so the material used for them must have a reduced conductor resistance, namely a high conductivity, and thus the development of copper alloys to replace low-conductivity brass and phosphor bronze has become an urgent task. In addition, both strength/springiness and flexibility are indispensable at the time of the press-molding of pins, but making the molding size narrower and thinner becomes more necessary from a different standpoint than that up until now.
On the other hand, in automotive electronics, in order to handle increases in the number of circuits and mounting densities accompanying increasingly electronic control systems, the connectors mounted in automotive electronics must be made lighter and space-saving by making the connectors more compact, so for example, the width of a box-shaped female connector has been reduced from 2.3 mm, which was the mainstream ten years ago, to 0.64 mm at present. Naturally, high conductivity is required in the same manner as for portable electronics. In addition, in order to maintain good connection properties after being molded into a box-shaped connector, even though the sheet thickness is roughly 0.25 mm or nearly unchanged from in the past, strict shape tolerances are required, forcing the use of states where the inside radius R is nearly 0 or states of bending nearly to tight contact, and thus the working conditions are more strict than in the past.
Accordingly, if one wishes to improve conductivity even while achieving both good strength/springiness and bending workability, this cannot be achieved with brass or phosphor bronze or other materials that are solid-solution strengthened by the addition of large amounts of additive elements. Precipitation strengthening of materials is one example of a method of increasing the conductivity while also obtaining high strength and high springiness, but if precipitation strengthening is used, deterioration of the ductility and bending workability of the material is ordinarily not negligible, and when it is attempted to avoid this, the control of the amount of elements added and the working and heat treatment processes required to control the size and distribution of precipitates becomes complex and as a result the manufacturing costs become higher (as in patent document JP2000-80428A, for example). As one method still remaining for solid-solution strengthened materials, measures can be taken to suppress the amount of solid-soluble elements added that lead to decreased conductivity, and to modify the machining and heat-treatment processes, but reducing the solid-solution strengthening elements leads to reduced strength so one must rely on that much more on work hardening, so decreased ductility and formability are unavoidable. At any rate, there has been a need to establish methods of evaluation from unconventional standpoints and adopt measures that extend the field of view to standpoints based on studies of texture, but no dramatic improvements have been achieved.
As a result of extensive studies performed in order to solve the problems of the background art described above, the material used for narrow-pitch connectors and automotive box connectors, which are blanked to the desired shape by means of high-speed press-molding using dies, is forced to assume the state where the inside radius R of the box portion is nearly 0 or the state of bending nearly to tight contact as the terminals tend to become thinner and narrower, or more specifically the spring portion becomes 0.10-0.25 mm thick and 0.10-0.30 mm wide, and so how to achieve superior bending workability while maintaining high strength came up as an important problem to be solved from the standpoint of properties. Regarding bending workability in particular, the state of stress on the convex surface of a bend at the time of bending varies depending on the width/thickness ratio W/t (the ratio of the test piece width W to the sheet thickness t) from tension in a single axis to surface-strain tension, so it is mandatory to improve the bending workability in consideration of the surface-strain tension accompanying the deterioration of bending workability.